Web Application Projects Add-On Installation Issue/Solution

Issue: A small set of users installing the Visual Studio 2005 Web Application Projects Add-On experience the following installation error:

Unable to get installer types in the C:\Program Files\Microsoft Visual Studio 8\Common7\IDE\Microsoft.VisualStudio.Web.Application.dll assembly. --> Unable to load one or more of the requested types.
Retrieve the LoaderExceptions property for more information.

When this occurs on a given machine, it will re-occur every time the user attempts to re-install.  Users have attempted uninstalling Visual Studio 2005, Visual Studio 2003, and other applications and patches without having any effect.  Other machines in the same office will install fine from the same MSI file.

Cause: The root cause of this problem has not been found.  It is rare and we have not been able to reproduce it locally.  Information gathered about affected machines do not indicate any outstanding common factors.  The effective cause if the failure of a Custom Action at the end of the installation sequence which is intended to invoke Visual Studio with a command switch which will set up the templates which were just installed.

Work-Around: Since this is the last action in the installation sequence, and there are no Custom Actions triggered by “commit”, it is possible to work around this error by disabling installation rollback.  At this point of the installation all code and data has been installed, and all registration is complete.  The trick is simply to skip the rollback caused by the failure of the Custom Action, and then to execute the equivalent manually.

Note: only use this workaround for the exact issue describe above.  Disabling rollback of installations is not generally recommended!  It is acceptable in this case because the error occurs as the last action in the installation.

1. Install the update from the command line:
   msiexec /i WebApplicationProjectSetup.msi DISABLEROLLBACK=1
   (Note that the case of DISABLEROLLBACK is significant.)
2. Reboot the computer.
3. Open a command window and execute:
   C:\Program Files\Microsoft Visual Studio 8\Common7\IDE\devenv.exe /setup
   (Adjust as necessary for your installation location.)
4. Start Visual Studio and verify that the menu command New|Project.. displays a Web node under both the Visual Basic and CSharp nodes in the left-hand pane.  Create an ASP.Net Web Application and ensure that it will compile and run.

Let me know if you experience any problems with this approach, or have any information that might help lead to the root cause.